Dyeing of polyesters with vat dyes



United States Patent DYEING or POLYESTERS WITH VAT DYES Jerry M. Mecco,Somerville, and Joseph W. Creely, East Bound Brook, N. J., assignors toAmerican Cyanamid Company, New York, N. Y., a corporation of Maine NoDrawing. Application May 17, 1952,

' Serial No. 288,544

2 Claims. (Cl. 834) failed to dye polyester fibers, and so thisimportant field of dyestuffs has been unusable. According to the presentinvention, we have found that it is possible to dye polyester fiberswith vat dyestuffs under certain very definite conditions. The mostimportant is the pH of the dye bath which must be between 6 and 8, andprefwith standard conventional practice.

erably between 6.5 and 7.5. At this pH, vat dyestufis j are reduced totheir leuco compounds in the form of socalled vat acids in which thehydroxyl groups are free rather than the sodium salts which 'areproduced in the ordinary vats. It is not known why the vat acidssocalledfor they are not true acids except in the sense that phenols aresometimes called acids because they react with strong bases to formsalts-behave in such a satisfactory manner in dyeing polyester fibersWhere they will not dye practically cellulose as cotton and viscoserayon. It is not known what the reason is for this anomalous behavior.

The present invention requires the definite pH range. However, it is notimportant to the operativeness of the process how the range is obtainedand maintained. It is perfectly possible to use strong alkali aqueoussolutions of caustic soda. However, this requires rather carefulsupervision of the dyeing process because the pH of the dye bath tendsto change as the reducing agent, normally sodium hydrosulfite, becomesoxidized to sodium bisulfate and thus reduces the pH. Therefore, in thepreferred embodiment of the present invention bufiiers are used toautomatically maintain the desired pH range; preferably these arepolyphosphate buffers such as sodium tripolyphosphate or sodiumtetraphosphate. When a buffer is used, it is not necessary to providecare ful supervision and control in order to maintain the pH. Of the twobuffers, sodium tripolyphosphate is somewhat the better.

The second condition which is necessary to the present invention is ahigh temperature. Satisfactory results are not obtained if the dyeing iseffected below the boiling point of water. Even at the boil the dyeingis slow and with some dyes the levelness leaves something to be desired.Excellent results are obtainable at higher temperatures, preferably fromabout 250 F. to 290 F. The upper limit on temperatures i not criticaland is determined by a temperature which the polyester fibers 'willstand. As a practical matter, temperatures above 325 F. are too high andtend to damage the fibers.

The invention will be described more fully in conjunction with thefollowing specific examples, the parts being by weight unless otherwisespecified.

Example 1 A staple polyglycol-terephthalate yarn normally sold PatentedDec. 18, 1956 2 under the trade-name Dacron was dyed using 10% by weightof 6,6'-dichloro-4,4' dimethyl-2,2'-bis thionaphthene indigo in a bathhaving a 10:1 water ratio and containing 6% sodium tripolyphosphate and4% sodium hydrosulfite. The dye was then oxidized by boiling with adilute 13% hydrogen peroxide solution containing 1% acetic acid. Thedyeing took only a few minutes at 290 F. and a bright pink shaderesulted. Microscopic examination showed that the fibers were wellpenetrated. After dyeing the staple was washed with water and then witha solution of sodium dodecyl sulfate in accordance Example 2 Theprocedure of Example 1 was followed at 250 F. A good dyeing wasobtainable but the dyeing time was about 12 times as long.

. Example 3 The procedure of Example 1 was followed with Dacron filamentyarn using3% sodium tripolyphosphate and 2% sodium hydrosulfite. Thesame results were obtained as with the staple yarn, microscopic exam'nation showing good penetration.

Example 4 The procedure of Example 3 was followed but the dyeing waseffected at a lower temperature of 250 F. The results were the same butthe dyeing time was very markedly extended.

Example 5 The procedure of Example 1 was followed but in- .stead ofusing the tripolyphosphate, sufiicient amount of 30 B. aqueous sodiumhydroxide was employed to bring the bath to a pH of between 6.5 and 7.5,the results being identical.

Example 6 The procedure of Example 1 was followed but the pink vatdyestutf was replaced by a corresponding amount of Vat Green Color IndexNo. 1184. A well-penetrated green dyeing resulted.

Example 8 The procedure of Example 7 was repeated at 250 F. The resultsobtained were the same but the dyeing time was greatly extended.

Example 9 5 parts of a skein of Dacron staple yarn was dyed in a bathcontaining 10% of Jade Green (dimethoxydibenzanthrone), 3% sodiumtripolyphosphate and 2% sodium hydrosulfite, the bath fiber ratio being10:1. The dyeing was complete in a few minutes at 290 F. and then theyarn was removed and boiled in a 1% aqueous sodium carbonate solutionand oxidized by boiling with dilute, (0.3%) hydrogen peroxide solutioncontaining 1% acetic acid. A deep blue green color resulted which wasfast to washing when boiled for 10 minutes in a bath containing 0.25%sodium dodecyl sulfate and 0.25% acetic acid.

Example 10 The procedure of Example 1 was followed except that thetemperature was reduced to 250 F. and the dyeing time increased 12times. A blue green dyeing was obtained which on microscopicalexamination showed that 3 the dye had penetrated into the fibers. Thedyeing, however, was not as strong and the penetration not as deep as inExample 1.

Example 11 5 parts of a skein of Dacron staple yarn was dyed in a bathcontaining 5% Hydron Pink FF (6,6'-dichloro- 4,4-dimethyl-2,2-bisthionaphthene indigo), 3% sodium tripolyphosphate, 2% sodiumhydrosulfite and 1% aluminum chloride with 6 mols of water ofcrystallization, the bath having a bath-fiber ratio of 10:1. The dyeingproceeded very rapidly at 290 F. After completion of the dyeing theskein was removed from the bath and boiled with 1% aqueous sodiumcarbonate solution followed by oxidizing by boiling with 1 part of a 3%hydrogen peroxide solution containing 1% acetic acid. The skein was thenWashed in a boiling water solution containing 0.25% sodium dodecylsulfate and 0.25% acetic acid. A bright pink dyeing resulted, the fibersbeing well penetrated when examined under the microscope.

Example 12 The procedure of Example 11 was followed, substituting forthe Hydron Pink the blue dye CI No. 1184 and replacing the aluminumchloride with an equivalent amount of zirconium oxychloride. A deep bluedyeing resulted, showing good penetration.

We claim:

1. A process of dyeing fibrous polyesters of a glycol and apolycarboxylic acid with vat dyes, which comprises heating the saidpolyester fibers in an aqueous dyebath containing an unesterified leucovat dye, a reducing agent and sodium tripolyphosphate, and having a pHbetween 6.5 and 7.5, at a temperature between the boiling point of waterand 290 F., the pH of the aqueous dyebath during dyeing being maintainedbetween 6.5 and 7.5 by means of the sodium tripolyphosphate buffer, andoxidizing the dyestufi? on the fiber after dyeing is complete.

2. The process of claim 1 wherein said polyester fiber is a polyglycol-terephthalate fiber.

UNITED STATES PATENTS References Cited in the file of this patent1,900,168 Dreyfus Mar. 7, 1933 1,900,172 Ellis Mar. 7, 1933 2,627,449Luttringhaus Feb. 3, 1953 OTHER REFERENCES Chem. Tech. of Dyeing andPrinting, by L. Diserens, published New York City, 1948, by ReinholdPublishing Corporation, pages and 136.

American Dyestufi Reporter for January 22, 1951, pages PS1 to P54inclusive.

American Dyestutf Reporter for October 15, 1951, pages P681 to P684inclusive.

1. A PROCESS OF DYEING FIBROUS POLYESTERS OF A GLYCOL AND APOLYCARBOXYLIC ACID WITH VAT DYES, WHICH COMPRISES HEATING THE SAIDPOLYESTER FIBERS IN AN AQUEOUS DYEBATH CONTAINING AN UNESTERIFIED LEUCOVAT DYE, A REDUCING AGENT AND SODIUM TRIPOLYPHOSPHATE, AND HAVING A PHBETWEEN 6.5 AND 7.5, AT A TEMPERATURE BETWEEN THE BOILING POINT OF WATERAND 290* F., AND PH OF THE AQUEOUS DYEBATH DURING DYEING BEINGMAINTAINED BETWEEN 6.5 AND 7.5 BY MEANS OF THE SODIUM TRIPOLYPHOSPHATEBUFFER, AND OXIDIZING THE DYESTUFF ON THE FIBER AFTER DYEING ISCOMPLETE.